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Sensitization
Sensitization is a non-associative learning process in which repeated administrations of a stimulus results in the progressive amplification of a response.Shettleworth, S. J. (2010) "Cognition, Evolution and Behavior" (2nd Ed) New York:Oxford Sensitization often is characterized by an enhancement of response to a whole class of stimuli in addition to the one that is repeated. For example, repetition of a painful stimulus may make one more responsive to a loud noise. Neural substrates of sensitization The neural basis of behavioral sensitization is often not known, but it typically seems to result from a cellular receptor becoming more likely to respond to a stimulus. Several examples of neural sensitization include: * Electrical or chemical stimulation of the rat hippocampus causes strengthening of synaptic signals, a process known as long-term potentiation or LTP.Collingridge GL, Isaac JT, Wang YT (2004). "Receptor trafficking and synaptic plasticity". Nat Rev Neurosci 5(12): 952–962, PMID 15550950, . LTP of AMPA receptors has been proposed as a potential mechanism underlying memory and learning in the human brain. * In "kindling", repeated stimulation of hippocampal or amygdaloid neurons in the limbic system eventually leads to seizures in laboratory animals. After sensitization, very little stimulation may be required to produce seizures. Thus, kindling has been suggested as a model for temporal lobe epilepsy in humans, where stimulation of a repetitive type (flickering lights for instance) can cause epileptic seizures.Morimoto K, Fahnestock M, Racine RJ (2004). "Kindling and status epilepticus models of epilepsy: Rewiring the brain". Prog Neurobiol 73(1): 1–60, PMID 15193778, . Often, people suffering from temporal lobe epilepsy report symptoms of negative effects such as anxiety and depression that might result from limbic dysfunction.Teicher MH, Glod CA, Surrey J, Swett C, Jr (1993). "Early childhood abuse and limbic system ratings in adult psychiatric outpatients". J Neuropsychiatry Clin Neurosci 5(3): 301–306, PMID 8369640. * In "central sensitization," nociceptive neurons in the dorsal horns of the spinal cord become sensitized by peripheral tissue damage or inflammation.Ji RR, Kohno T, Moore KA, Woolf CJ (2003). "Central sensitization and LTP: Do pain and memory share similar mechanisms?". Trends Neurosci 26(12): 696–705, PMID 14624855. This type of sensitization has been suggested as a possible causal mechanism for chronic pain conditions. The changes of central sensitization occur after repeated trials to pain. Research from animals has consistently shown that when an trial is repeatedly exposed to a painful stimulus, the animal’s pain threshold will change and result in a stronger pain response. Researchers believe that there are parallels that can be drawn between these animal trials and persistent pain in people. For example, after a back surgery that removed a herniated disc from causing a pinched nerve, the patient may still continue to “feel” pain. Also, newborns who are circumcised without anesthesia have shown tendencies to react more greatly to future injections, vaccinations, and other similar procedures. The responses of these children are an increase in crying and a greater hemodynamic response (tachycardia and tachypnea).Gudin J. (2004). Medscape Neurobiology: Expanding Our Understanding of Central Sensitization. Medscape: Medscape Education. * Drug sensitization occurs in drug addiction, and is defined as an increased effect of drug following repeated doses (the opposite of drug tolerance). Such sensitization involves changes in brain mesolimbic dopamine transmission, as well as a molecule inside mesolimbic neurons called delta FosB. An associative process may contribute to addiction, for environmental stimuli associated with drug taking may increase craving. This process may increase the risk for relapse in addicts attempting to quit.Robinson TE, Berridge KC (1993). "The neural basis of drug craving: An incentive-sensitization theory of addiction". Brain Res Brain Res Rev 18(3): 247–291, PMID 8401595. * Allergic Sensitization – There is an acute response (early stages) and a late-phase response (later stages). In the early stages, the Antigen-Presenting Cell causes a response in a TH2 lymphocyte which produce the cytokine interleukin-4 (IL-4). The TH2 lymphocytes interact with B cells and together they produce IgE. IgE circulates around and binds to receptors of cells leading to an acute inflammatory response.Janeway, Charles; Paul Travers, Mark Walport, and Mark Shlomchik (2001). Immunobiology; Fifth Edition. New York and London: Garland Science. pp. e–book. ISBN 978-0-8153-4101-7. In this case, sensitization is commonly referring to commencement of allergic responses.Janeway C, Travers P, Walport M, Shlomchik M, eds. (2001). Immunobiology 5: The Immune System in Health and Disease. New York: Garland Pub., ISBN 0-8153-3642-X Allergic sensitization development varies with age, with younger children are at the greatest risk of developing allergic sensitization.Croner S (1992). "Prediction and detection of allergy development: influence of genetic and environmental factors". J. Pediatr. 121 (5 Pt 2): S58–63. doi:10.1016/S0022-3476(05)81408-8. PMID 1447635. There are a variety of tests to diagnose allergic conditions. Tests that are commonly used place potential allergens on the skin of the patient and looking for a reaction to look for an allergen-specific IgE (Immunoglobulin E). They have shown that IgE levels are at their greatest before 10 years of age and fall vastly until one reaches 30. There is a school of thought that believes that there are different genetic loci for different ethnicities for the same inflammatory disease.De Swert LF (1999). "Risk factors for allergy". Eur. J. Pediatr. 158 (2): 89–94. doi:10.1007/s004310051024. PMID 10048601. By this thought, asthma has different chromosomal locations in people of European, Hispanic, Asian, and African descent.Barnes KC, Grant AV, Hansel NN, Gao P, Dunston GM (2007). "African Americans with asthma: genetic insights". Proc Am Thorac Soc 4 (1): 58–68. doi:10.1513/pats.200607-146JG. PMC 2647616. PMID 17202293. Archived from the original on 2010-11-16. Etiology Sensitization has been implied as a causal or maintaining mechanism in a wide range of apparently unrelated pathologies including substance abuse and dependence, allergies, asthma, and some medically unexplained syndromes such as fibromyalgia and multiple chemical sensitivity. Sensitization has also been suggested in relation to psychological disorders such as post-traumatic stress disorder, panic anxiety and mood disorders.Rosen JB, Schulkin J (1998). "From normal fear to pathological anxiety". Psychol Rev 105(2): 325–350, PMID 9577241.Antelman SM (1988). "Time-dependent sensitization as the cornerstone for a new approach to pharmacotherapy: drugs as foreign/stressful stimuli". Drug Development Research 14: 1–30.Post RM (1992). "Transduction of psychosocial stress into the neurobiology of recurrent affective disorder". Am J Psychiatry 149(8): 999–1010, PMID 1353322. History Eric Kandel was one of the first to study the neural basis of sensitization based on his experiments observing gill withdrawal of the seaslug Aplysia in the 1960s and 1970s. Kandel and his colleagues showed that after habituation from siphon touching (gill withdrawal response weakened), applying a paired noxious electrical stimulus to the tail and a touch to the siphon, gill withdrawal was once again noted. After this sensitization, applying a light touch to the siphon, absent of noxious stimulus to the tail, Aplysia produced a strong gill withdrawal response. When tested several days after the initial trials, this response was still manifest (After Squire and Kandel, 1999Squire LR, Kandel ER (1999). Memory: From Mind to Molecules. New York: Scientific American Library; New York: W.H. Freeman. ISBN 0-7167-6037-1.). In 2000, Eric Kandel was awarded the Nobel Prize in Physiology or Medicine for his research in neuronal learning processes. See also * Dishabituation * Habituation * Long-term potentiation * Synaptic plasticity * Neuroplasticity * Multiple Chemical Sensitivity References * Antelman, S.M. (1988). Time-dependent sensitization as the cornerstone for a new approach to pharmacotherapy: drugs as foreign/stressful stimuli. Drug Development Research, 14, 1-30. * Bell, I.R., Hardin, E.E., Baldwin, C.M., & Schwartz, G.E. (1995). Increased limbic system symptomatology and sensitizability of young adults with chemical and noise sensitivities. Environmental Research, 70, 84-97. * Collingridge, G.L., Isaac, J.T.R., & Wang, Y.T. (2004). Receptor trafficking and synaptic plasticity. Nature Reviews, 5, 952-962. * Ji, R., Kohno, T., Moore, K.A. & Woolf, C.J. (2003). Central sensitization and LTP: do pain and memory share similar mechanisms? Trends in Neurosciences, 26, 696-705. Full text * Kandel, E.R. (2004). The molecular biology of memory storage: a dialog between genes and synapses. Bioscience Reports, 24, 477-522. Full text * McEachern, J.C. & Shaw, C.A. (1999). The plasticity-pathology continuum: defining a role for the LTP-phenomenon. Journal of Neuroscience Research, 58, 42-61. * Morimoto, K., Fahnestock, M. & Racine, R.J. (2004). Kindling and status epilepticus models of epilepsy: rewiring the brain. Progress in Neurobiology, 73, 1-60. * Post, R.M. (1992). Transduction of psychosocial stress into the neurobiology of recurrent affective disorder. American Journal of Psychiatry, 149, 999-1010. Abstract * Rosen, J.B. & Schulkin, J. (1998). From normal fear to pathological anxiety. Psychological Review, 105, 325-350. Further reading * Antzoulatos, E.G., Wainwright, M.L., Cleary, L.J., & Byrne, J.H. (2006). Long-term sensitization training primes Aplysia for further learning. Learning & Memory, 13, 422-425. Full text * Barbas, D., DesGroseillers, L., Castellucci, V.F., Carew, T.J., & Marinesco, S. (2003). Multiple Serotonergic Mechanisms Contributing to Sensitization in Aplysia: Evidence of Diverse Serotonin Receptor Subtypes. Learning & Memory, 10, 373 - 386. Full text * Burrell, B.D. & Sahley, C.L. (1998). Generalization of Habituation and Intrinsic Sensitization in the Leech. Learning & Memory, 5, 405 - 419. Full text * Burrell, B.D. & Sahley, C.L. (1999). Serotonin Depletion Does Not Prevent Intrinsic Sensitization in the Leech. Learning & Memory, 6, 509 - 520. Full text * Hawkins, R.D., Cohen, T.E., & Kandel, E.R. (2006). Dishabituation in Aplysia can involve either reversal of habituation or superimposed sensitization. Learning & Memory, 13, 397-403. Full text * Kaplan, P.S., Goldstein, M.H., Huckeby, E.R., & Cooper, R.P. (1995). Habituation, sensitization, and infants' responses to motherese speech. Developmental Psychobiology, 28, 45-57. Full text * McSweeney, F.K., Hinson, J.M, & Cannon, C.B. (1996). Sensitization-habituation may occur during operant conditioning. Psychological Bulletin, 120, 256-271. Full text * Overmier, J. B. (2002). Sensitization, conditioning, and learning: Can they help us understand somatization and disability? Scandinavian Journal of Psychology, 43, 105-112. Full text * Philips, G.T., Tzvetkova, E.I., Marinesco, S., & Carew, T.J. (2006). Latent memory for sensitization in Aplysia. Learning & Memory, 13, 224 - 229. Full text * Shum, F.W.F., et. al. (2007). Alteration of cingulate long-term plasticity and behavioral sensitization to inflammation by environmental enrichment. Learning & Memory, 14, 304 - 312. Abstract * Sutton, M.A., Ide, J., Masters, S.E., & Carew, T.J. (2002). Interaction between Amount and Pattern of Training in the Induction of Intermediate- and Long-Term Memory for Sensitization in Aplysia. Learning & Memory, 9, 29 - 40. Full text Category:Sensory system Category:Learning